Lower Prefrontal fNIRS Activation Can Occur Without Worse Stroop Scores

A 2026 study found lower activation in selected left prefrontal channels among abstinent participants with severe methamphetamine use disorder, despite no significant differences in conventional Stroop performance. Brain-signal differences and behavioral deficits were separate findings.

What the investigators measured

Luo and colleagues compared 73 abstinent participants with severe methamphetamine use disorder and 51 healthy controls. Functional near-infrared spectroscopy, or fNIRS, measured task-related hemodynamic responses during a Stroop task. This was observational human research, not an experimental methamphetamine challenge.

The regional finding survived specified checks

Lower activation in channels 32 and 43 within the left dorsolateral prefrontal cortex was reported after correction across channels. The differences remained after adjustment for education and alcohol-screening scores. That supports the specified regional result while leaving other unmeasured group differences possible.

Abstinence was a moderator, not a simple recovery clock

Duration of abstinence modified the relationship between channel 43 activation and a reaction-time difference score. It was not directly correlated with channel 43 activation. A moderation result therefore cannot be rewritten as evidence that activation steadily normalizes with each additional day without use.

The measurement boundary

fNIRS estimates changes in oxygenation-related optical signals. It does not measure methamphetamine in brain tissue or in forensic whole blood. With nonsignificant conventional behavioral differences, the study cannot support a claim that the imaging finding alone demonstrated worse task performance in every participant. Cross-sectional comparisons also do not trace within-person recovery. No individual drug-detection or driving-impairment cutoff was validated; the result is a group-level dissociation between physiology and tested behavior.

Related evidence

For a different perspective on interpreting stimulant evidence, see our analysis of the Swedish amphetamine concentration study. Its study population and outcome should remain separate from the present findings.

Primary research

Abnormal DLPFC activation in severe methamphetamine use disorder during abstinence: fNIRS evidence from Stroop task. Original human research. doi:10.3389/fpsyt.2026.1863806.